L-Arginine is a basic, semi-essential amino acid that was discovered in 1886 in lupin seedlings and then in 1895 in mammalian protein (Boger & Bode-Boger 2001). For humans L-arginine is considered to be a semi-essential amino acid or a conditionally essential amino acid, as requirements may increase during metabolic stress or when there is insufficient endogenous L-arginine for optimal growth or tissue repair; for birds and carnivores it is an essential amino acid. It is also the most abundant nitrogen carrier in animals and humans.